Payload Controller Schematics

Introduction

UMS-0005-HW (payload imaging controller) is an electrical hardware (HW) assembly, designed to mount the Iris Payload cameras and associated control circuits. The Payload Controller is responsible for processing incoming commands received over CAN bus to obtain images from one of two cameras, store RAW image data and transmit image data over CAN bus, when requested.

Figure 1: Board Drawing Sheet 1

Figure 2: Board Drawing Sheet 2

Design Description

Figure 3 shows the simplified block diagram of the payload camera controller. The camera modules (CAM1 & CAM2) are compatible with the Digital Camera Module Interface (DCMI) standard and used to send image data to the processor (STM32F765). The primary function of the payload imaging controller is to capture and save images of the payload from one of two MT9D111 camera modules. Since the MT9D111 is compatible with the DCMI standard, the STM32F765 MCU which offers an embedded DCMI controller was selected, eliminating the need for a discrete FIFO buffer. The STM32F765 also embeds a flexible memory controller (FMC), control area network (CAN) controller, Inter-integrated circuit (I2C) interface and Analog to Digital converter (ADC), as well as General purpose I/Os that are used in this application. Table 1 provides a summary of interface functionality. External interfaces of the payload imaging controller are obtained from the spacecraft harness. These bring Power and CAN bus into board.

Figure 3. UMS-0005 Simplified Block Diagram

Table 1: summary of MCU interface functions

summary of MCU interface functions

Payload imaging

Figure 4 shows a block diagram of the components and interfaces involved in payload image capture and transmission. Following are sequences for image capture, storage, retrieval and transmission

Figure 4. payload imaging components and transfer interfaces

Simplified Image capture and storage sequence:

1. Payload controller receives request via CAN bus to capture image

2. Image capture sequence initiated by STM32 via I2C.

3. Camera decodes I2C command and prepares image

4. Camera transmits image to STM32 via DCMI

5. STM32 Buffers image and transmits to NAND FLASH via FMC interface

Simplified Image retrieval and transmission sequence:

1. Payload controller receives request via CAN bus to transmit image

2. STM32 retrieves image from NAND FLASH via FMC interface

3. STM32 transmits image through CAN transceiver on CAN bus

Camera Selection:

The STM32 embeds only one DCMI controller. As such, the DCMI interfaces of both cameras are multiplexed into the STM32 as in Figure 5. Image capture requests received via CAN bus must specify which one of two cameras should be used. Using GPIO interfaces, the STM32 can select which camera to turn on and connect the DCMI controller through the MUX.

Figure 5. Camera Multiplexing

Temperature monitoring

The payload imaging controller is expected to monitor two NTC type thermistors placed close to it. The NTC output is converted from resistance to analog voltage using a bridge circuit and amplifier before sampling into the ADC of the STM32 as in Figure 6.